In recent years, wearable computers, which are worn on the body to allow hands-free operation, have been developed in a variety of fields. The recent progress of semiconductor technology and communications technology has allowed wearable computers to utilize a network as a means for computation and storage which were previously performed by the wearable computers themselves. Therefore, a main function of wearable computers which will be required in the future is one that relates to human-machine interface (i.e., an input device and an output device). As the output device, some head-mounted displays or bone conduction headphones have already been developed, for example. However, no low-cost input device which is suitably used in wearable computers has been developed yet.
On the other hand, although it is not used as an input device for wearable computers, there is a device for measuring the number of chewing cycles in human mastication (see, for example, Patent Documents 1-3). This device can acquire information in a hands-free manner.
When a human chews food etc., the movement of the jaw is accompanied by the movement of muscles around the ear canal. Therefore, in the device of Patent Document 1, a pressure sensor is inserted in the ear canal to sense a change in pressure in the ear canal which is caused by the muscle movement, thereby measuring the number of pressure changes as the number of chewing cycles.
Patent Document 2 is based on a principle similar to that of Patent Document 1. Patent Document 2 describes a low pressure sensor, a piezoelectric sensor, and a press sensor which are used as a pressure sensor to sense a movement of the ear canal associated with mastication.
Patent Document 3 is also basically based on a principle similar to that of Patent Documents 1 and 2. Patent Document 3 describes a sensor which senses a movement derived from mastication, and also describes, as examples of the sensor, a tension sensor, an electromyography sensor, and a pressure sensor.